Mechanisms of Evolution AP Biology Chapter 22

Endless Forms Most Beautiful A new era of biology began in 1859 when Charles Darwin published The Origin of Species The Origin of Species focused biologists’ attention on the great diversity of organisms

Darwin noted that current species are descendants of ancestral species Evolution can be defined by Darwin’s phrase “descent with modification” Species are descendants of ancestral species that were different from the present-day species

giant sloths to small sloths Height: up to 20″ Weight: up to 10 lbs. Lifespan: years exotic-pet-choices-for-the-future/

More narrow definition Evolution is a change in the genetic composition of a population from generation to generation Did Darwin know this?

Evolution can be viewed as both a pattern and a process: pattern - data accumulated process - mechanisms in place to cause change

Prevailing ideas about the origin of life Species were fixed and individually created The earth was only 6000 years old

Fig American RevolutionFrench RevolutionU.S. Civil War – The Origin of Species is published. Wallace sends his hypothesis to Darwin. Darwin begins his notebooks. Darwin writes essay on descent with modification. Darwin travels around the world on HMS Beagle. Malthus publishes “Essay on the Principle of Population.” Lyell publishes Principles of Geology. Lamarck publishes his hypothesis of evolution. Hutton proposes his theory of gradualism. Linnaeus (classification) Cuvier (fossils, extinction) Malthus (population limits) Lamarck (species can change) Hutton (gradual geologic change) Lyell (modern geology) Darwin (evolution, natural selection) Wallace (evolution, natural selection) Climate of the times

People and ideas that influenced Darwin

The Greek philosopher Aristotle viewed species as fixed and arranged them on a scala naturae The Old Testament holds that species were individually designed by God and therefore perfect

Carolus Linnaeus interpreted adaptations as evidence that the Creator had designed each species for a specific purpose Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying organisms

Fig Younger stratum with more recent fossils Layers of deposited sediment Older stratum with older fossils The study of fossils helped to lay the groundwork for Darwin’s ideas

Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier Cuvier advocated catastrophism, speculating that each boundary between strata represents a catastrophe

Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today. Hutton called his ideas gradualism. Lyell’s principle of uniformitarianism states that the mechanisms of change are constant over time This view strongly influenced Darwin’s thinking

Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics The mechanisms he proposed are unsupported by evidence However, he did come up with a mechanism for evolution.

Was Lamarck totally wrong?

A study shows that when mice are taught to fear an odor, both their offspring and the next generation are born fearing it. The gene for an olfactory receptor activated by the odor is specifically demethylated in the germ line and the olfactory circuits for detecting the odor are enhanced.

About Darwin As a boy and into adulthood, Charles Darwin had a consuming interest in nature Darwin first studied medicine (unsuccessfully), and then theology at Cambridge University After graduating, he took an unpaid position as naturalist for a 5-year around the world voyage on the Beagle

Fig NORTH AMERICA EUROPE AFRICA AUSTRALIA GREAT BRITAIN SOUTH AMERICA ATLANTIC OCEAN PACIFIC OCEAN Cape of Good Hope Tierra del Fuego Cape Horn Tasmania New Zealand Andes Equator The Galápagos Islands Pinta Marchena Genovesa Santiago Daphne Islands Pinzón Fernandina Isabela San Cristobal Santa Fe Santa Cruz Florenza Española His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America

Fig (a) Cactus-eater(c) Seed-eater (b) Insect-eater He noticed how finches’ beaks were adapted for their diet.

In 1844, Darwin wrote an essay on the origin of species and natural selection but did not introduce his theory publicly, anticipating an uproar In June 1858, Darwin received a manuscript from Alfred Russell Wallace, who had developed a theory of natural selection similar to Darwin’s Darwin quickly finished The Origin of Species and published it the next year

Let’s get together on this so we can both be famous!

The Origin of Species Darwin developed two main ideas: –Descent with modification explains life’s unity and diversity –Natural selection is a cause of adaptive evolution In the Darwinian view, the history of life is like a tree with branches representing life’s diversity Darwin’s theory meshed well with the hierarchy of Linnaeus

Fig. 22-7

Fig Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) Moeritherium Barytherium Deinotherium Mammut Elephas maximus (Asia) Stegodon Mammuthus Loxodonta africana (Africa) Loxodonta cyclotis (Africa) Millions of years ago Years ago Platybelodon

Adaptations Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection Darwin then described four observations of nature and from these drew two inferences

Observation #1: Members of a population often vary greatly in their traits

What is the ultimate source of variations in natural populations? MUTATIONS

Observation #2: Traits are inherited from parents to offspring Observation #3: All species are capable of producing more offspring than the environment can support

Observation #4: Owing to lack of food or other resources, many of these offspring do not survive My idea Precisely! MALTHUS

Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals (fitness) Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations ***Favorable – NOT BEST NECESSARILY

Darwin was influenced by Thomas Malthus who noted the potential for human population to increase faster than food supplies and other resources Struggle for survival

Individuals with certain heritable characteristics survive and reproduce at a higher rate than other individuals Natural selection increases the adaptation of organisms to their environment over time If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species…Nature selects individuals to survive. Individuals do not change to survive.

Fig (b) A stick mantid in Africa (a) A flower mantid in Malaysia

What is the relationship between evolution and natural selection? Natural selection is one mechanism that can result in the process of evolution.

One more important thing…. Populations evolve, NOT INDIVIDUALS! Natural selections acts on individuals but the population as a whole evolves!

Evidences for Evolution Direct observations The Fossil Record Homology Biogeography

1. Direct Evidences Today Ex- Evidence of Drug-resistant HIV Ex – Evidence of Drug-resistant bacteria such as MRSA Ex – Evidence of Pesticide-resistant insects Coloration patterns in guppies due to predation

Fig Weeks Patient No. 3 Patient No. 2 Patient No. 1 Percent of HIV resistant to 3TC

2. Fossil Evidence The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time

Fig Bristolia insolens Bristolia bristolensis Bristolia harringtoni Bristolia mohavensis Latham Shale dig site, San Bernardino County, California Depth (meters)

Fig (a) Pakicetus (terrestrial) (b) Rhodocetus (predominantly aquatic) (c) Dorudon (fully aquatic) Pelvis and hind limb Pelvis and hind limb (d) Balaena (recent whale ancestor)

3. Homology Homology is similarity resulting from common ancestry Can be both anatomical and molecular Anatomical similarities seen in comparative embryology suggest common ancestry NOVA | Guess the Embryo NOVA | The Zoo of You

Fig Humerus Radius Ulna Carpals Metacarpals Phalanges HumanWhale Cat Bat Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor

Fig Human embryoChick embryo (LM) Pharyngeal pouches Post-anal tail

Vestigial structures are remnants of features that served important functions in the organism’s ancestors Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor

Convergent evolution is the evolution of similar, or analogous, features in distantly related groups Analogous - having the same function but not necessarily evolutionarily related.

Fig Sugar glider Flying squirrel AUSTRALIA NORTH AMERICA

4. Biogeography Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution Islands have many endemic species that are often closely related to species on the nearest mainland or island

Bird Biogeography

Phylogeny – the evolutionary history of an organism Evolutionary trees show common ancestry and homologous structures linking organisms.

Evolutionary Tree

Is natural selection the ONLY mechanism responsible for evolution?